Nabil Bentaleb fighting for Tottenham career under Mauricio Pochettino

While the rest of Tottenham's squad were preparing for Saturday's huge north London derby -- arguably the biggest game in the history of the fixture -- Nabil Bentaleb spent Thursday afternoon on a coach to High Wycombe.

Bentaleb had, according to Mauricio Pochettino, asked to play in the under-21 match against Reading to improve his fitness -- incidentally, the same thing the head coach said about Andros Townsend shortly before the winger was sold to Newcastle.

"Football is present. He asked for the under-21s and we gave him the possibility because he wasn't on the squad list. There's no problem," Pochettino explained on Thursday.

The Algerian was replaced on the hour but has no chance of being involved in Saturday's high-intensity derby at White Hart Lane, even with Mousa Dembele a doubt.

Bentaleb's demotion is the latest setback for a player who began the season with the ink still drying on a new five-year contract on vastly improved terms. He has since made just five league appearances.

A year ago, the idea of a fit and rested Bentaleb missing Spurs' biggest game of the season was unthinkable. He was the embodiment of Pochettino's philosophy and perhaps the club's player of last season behind Harry Kane.

Bentaleb's coming of age was the 2-1 win over Arsenal at White Hart Lane in February 2014, helping to contain and overrun a visiting midfield including Mesut Ozil, Santi Cazorla and Aaron Ramsey and assisting Kane's winner. The memory makes his absence on Saturday more poignant.

The rangy midfielder's demise dates back to August and a start to the season marred by bad form and bad luck.

His misplaced pass led to Manchester United's winner on the opening day and he was dropped for the subsequent draws with Stoke and Leicester before returning for the draw with Everton. He picked up an ankle injury after the match, and has not started another league game this season.

The simple explanation is that others excelled in his absence, particularly Eric Dier and Dele Alli, whose stunning rises seemed unlikely in August.

"From the beginning, he missed 17, 18 games with an injury and the team grew up and different players had the possibility to play and show quality like Eric Dier, Mousa Dembele or Tom Carroll," Pochettino said in January of a fit-again Bentaleb.

"We have a lot of midfielders. We keep a very good relationship with Nabil but it's true that if he works in the next few weeks, he always will have the possibility to show his real quality. It's about time for him to show he deserves to play. Always it's about football decisions."

There are other factors too. In June, Bentaleb went public with his frustration over delays in contract negotiations,admitting he was "tired" with the talks. The interview, at odds with Pochettino's mantras of "respect" and "togetherness", did not impress the club.

While Nacer Chadli and Ryan Mason, both injured for a similar period, quickly played themselves back into contention, Benatleb has struggled to impress on his rare outings.

Nabil Bentaleb has featured in just five Premier League matches this season.

He replaced Dier before half-time in his comeback game against Monaco in December but finished the match with little to show besides a yellow card. He did not feature again for another month.

When he returned to the starting lineup for the FA Cup trip to Colchester in January, he was again over-eager and in his only other start, in the 1-0 defeat to Crystal Palace in the following round, he struggled to cope with the Eagles' intensity and physicality.

Pochettino has tended to rotate in the Europa League, so Thursday's trip to Borussia Dortmund will be a better indicator of Bentaleb's standing than Saturday's season-defining match.

Bentaleb remains a highly rated and well-regarded member of the squad and there's a strong case that he brings more to the team than both Mason and Carroll.

Pochettino, however, has built his success on ruthlessly shaping his squad in his own image and there have been a number of high-profile casualties already. It's not farfetched to think Bentaleb could be next.